The present invention relates generally to system cooling techniques. In particular, embodiments of the present invention provide a method and system for providing an alternate cooling to an outdoor shelter housing electrical equipment. Merely by way of example, the invention has been applied to telecommunications shelters, but it would be recognized that the invention has a much broader range of applicability.
Telecommunication (telecom) shelters are typically constructed as an outdoor facility in either steel or pre-cast concrete structure for housing an electrical system. Physical dimensions for such shelters are about 20 ft in length, 10 ft in width, 10 ft in height with an access door and several access hatches for cable access. These shelters are usually attached to split system air-conditioning units for providing cooling for the electrical system therein. A conventional air conditioning (A/C) system associated with the shelter is typically powered from standard Alternating Current (AC) power supply and hence only operates and provides cooling as long as there is AC power available.
However, the electrical system within the telecom shelter usually needs to operate from a Direct Current (DC) voltage converted from the AC input by one or more DC power supplies disposed inside the shelter. This DC voltage is typically +24 VDC or −48 VDC and there are typically banks of batteries provided in the shelter to store this DC Power. The batteries are installed so that the systems can operate during events where the AC power is interrupted to the shelter. Cooling for outdoor telecom shelters is critical for proper operation of the electronics housed therein. Typically the telecom equipment installed in the shelters has an over-temperature shutdown monitor built into the equipment. Thus, the time that the telecom systems can operate is not limited by the battery life, but is limited by the time that the system can operate before it reaches the over-temperature shutdown threshold when the A/C system for providing cooling to the shelter is no longer functioning. This time depends on the external ambient conditions but is typically quite short ( approx 20 minutes to 1 hour) for conventional telecom shelter. One potential solution is to use a DC to AC inverter in the event of a standard AC power failure. However, this is considered to be not practical, because it would require a very large battery storage capability.
In conditions where a large amount of the telecom shelters lose power at the same time (such as in a hurricane event), the telecom equipment installed in the shelter is not available for subsequent rescue efforts. If cellular phone systems are used to communicate, 20 minutes is not enough time to restore power to so many systems. Due to a recent event that caused a sustained lack of communication (hurricane Katrina), the federal regulations have been changed. Telecom shelters are now required to operate for 4-8 hours after loss of standard AC power.
Therefore, an alternate system and method for providing cooling to the outdoor shelter of electrical equipment are desired.